It is highly desirable in the automotive industry to reduce pollutants emitted from an engine's exhaust. One way of achieving this goal is by means of a sensor, which can detect both the ethanol concentration and the volatility level of a particular fuel. By detecting these two variables, the engine can use a pre-programmed “look-up table” to select the best operation parameters, e.g., air/fuel ratios, timing of ignition start-up, etc., to generate a minimum amount of exhaust pollutants.
The sensor detects the fuel's ethanol concentration by determining the fuel's initial capacitance after first entering the sensor. The heater, which is attached to the sensor, then monotonically increases the sensor's temperature until most of the trapped fuel (e.g., greater than 80 wt %) is fully evaporated. As the fuel is evaporated, the fuel sample amount changes (the changes in capacitance) with the fuel temperature changes are detected by the sensor and are indicative of the fuel's volatility.
These sensors, however, have several drawbacks. First, the sensors comprise a large number of components, which increases the manufacturing costs of the sensors. Second, the sensors tend to be formed, at least in part, with glues, pastes, and other adhesives. As the fuels to which the sensors are exposed are solvents, they tend to destroy the glues and debond the heater and temperature sensor from the capacitance sensor. Third, the sensor is susceptible to thermal cycle fatigue as the thermal cycles, by which the sensor achieves its function, tend to destroy the glues holding the capacitance sensor to the temperature sensor and to the heater.